Process of separating oxides and gases from molten aluminum and aluminium alloys



. 7, 1933. R. STERNER-RAINER 0 PROCESS OF SEPARATING OXIDES AND GASESFROM MOLTEN ALUMINIUM AND ALUMINIUM ALLOYS Filed Jan. 14, 1932 PureHyena Comprc'sl' 7 a Waz'de orllecomposablz Chloride erda Bzflu orc'de Ilmlenzorl m% o p at? Patented Feb. 7, 1933 I UNITED mm PATENT oFrIcr-iROLAND s'ranxna-nmu, OI HEILBBONH-ON-TIIE-N Im', onmmr, ABIIGI'OBTQ mmLUBOI: MBPOB-LTION, O! NEW YORK, Y A CORPORATION 01 m YORK rnocrss orsmm'rme oxmlis m easns' m1 tom-air ALUIINIUI m ummmnr Annexe 7Application and January 14,1932, sex-m Io.

Various reports have been published on attempts aiming at separatinggases and oxides from aluminium alloys y passing a current of chlorinegas throu h the metal while in the molten state. It as also been roposedto erform the purifying process By means 0 chlorides, such as borontrichloride, vanadium chloride, titanium tetra-' chloride. While thetreatment with chlorine in many cases was not successful, the chloridesnamed are so expensive that they cannot be used per se in practice.Chloride of zinc which has been used for purifying molten aluminium fora long time past has remained the most suitable chloride and the onlyone in practical use up to the present time. Yet the purification bymeans of zinc chloride is not entirely perfect. Moreover it cannot beused for alloys which "are to remain free from zinc, for instancesilumin '(Si 13%, Al remainder), piston alloys, or aluminium alloysresisting corrosion, not only because by tie treatment with zincchloride these metals will be contaminated with zinc, but especiallybecause the alloy recovered from the residues contains so much zinc thatit cannot be used for-the same purpose.

The object of the present invention is a process for separating gases aswell as oxides from aluminium and aluminium alloys while in the moltenstate. For carrying on this process, those chlorides are added to themetal bath that vaporize at or shortly above the melting point ofaluminium or the aluminium alloys, for instance, at temperatures fromGOO-800. A portion of these chlorides suffer a thermal decompositionatthese temperatures, the compound v(1C1, for instance decomposing intogaseous chlorine on the one hand and carbon on the other hand. Theselection of the chloride is therefore to be made with the idea that:gaseous products will result, since the aim of the process requires thatbubbles be formed in the melt by 680,085, and in Germany January 17,1981.

the gases produced, so that in this way the impurities contained in themelt and in particular the unmelted impurities are removed. It has beenfound, however, that the treatment with chlorides alone which hasalready been proposed, is not suflicient to produce a comp ete removalof the impurities contained in t e melt and particularly of any gaseswhich may be dissolved'in the melt. For this purpose, the inventionprovides for the combination of the addition of chlorides with theaddition of volatile fluorides.- Suitable volatile fluorides arebifluoride of alkali metals and ammonium bifluoride. If a mixture ofthese substances, i. e., volatile or decom sable chlorides and volatilefluorides oft e group consisting of alkali metal and ammonium ifluoridesare brou ht to ether in the melt, the result is a puri ed an gasfreemetal which when cast yields dense castings. In this manner aurification of the molten metal can easily be attained to such anextent, that perfect castings can be made at only small expenditures. Ofthe chlorides which answer these requirements, first of all thosementionedabove are to be considered, i. e. boron trichloride, vanadiumchloride, titanium tetrachloride, and zinc chloride.

Also carbon tetrachloride, antimony pentachloride, silicon chloride,manganous chloride and chlorides of tin and iron may be applied forcarrying out the process according to the invention. Most of thesechlorides are known to have been used separately for the purpose ofpurifying metals, particularly for separating gases from moltenaluminium; however the present invention does not relate to using suchchlorides separately, but to u'sing-themin combination with alkalibifluorides.

Carbon tetrachloride was found to be suitable agent for separatingvoxides from the molten metals; it was however found, 00

that, in using this agent a significant separation of gases only tookplace, if there was taken a large amount, i. e. 415 cm.'/kg. of metaltreated or if the metal was treated a longer time for instance 20mintues .with this material. If however carbon tetrachloride is usedjointly with alkali bifluoride, especially immersing-bell, until thereaction had ceased.

with ammonium-bifluoride, it will be found that both gases and oxidescan be completely separated even from a highly contaminated and oxidizedmelt of aluminium in a short time with a small amount of the flux. In

place of carbon tetrachloride, antimony pentachloride or manganouschloride or an analogous compound of chlorine may be used with almostequally good success. These agents too, if used separately, effectuateup to a certain degree a separation of oxides, but only if the are usedjointly with alkali bifluoride wi l a good separation of both oxides andgases be attained.

The action of the aforesaid mixtures upon the metallic melts willhowever be considerably increased, if silicon chloride is added to thesemixtures. Though silicon chloride alone has ave strong purifying anddegasifying effect-,1t evolves by its action hydrochloric acid fumes insuch a quantity, that, when used by itself, it will raise practicaldifliculties. If however it is added to the aforesaid a cuts the actionof the latter can be increase by the silicon chloride, withouthydrochloric acid vapours being evolved to such an extent as to benoxious.

The small amount of purifying agents required in carrying out theprocess according to the invention deserves particular notice.

To prove this, a few examples may be disparticular case was pressed intothe molten metal at the same temperature by means of an About 200-300 g.of metal were treated in each case. Of the total of this treated metalasample of 100 g. was at once allowed to cool down in vacuo in apre-heated crucible, while another sample was taken 10 minutes later,during which waiting-time the melt in the furnace was constantly kept upat its temperature. This second sample was then 'metal. 4

The following results were obtained:

Comparative teats carried out with K. S. Seawateralloy of the oompoemonHa 2-87,, Mar 1.3%, St 0.2%. At remainder at 850' 0. temperature oftreatment namlm ranoeot No. Aaentuaed Time the Great number of abt. W70! the vm The name Without treatment Wlthout treatment 0.1 carbontetrachlo- 0.1 carbm tetrachlo- 1% aiitlmmy pmtlehlo- 1% ahtlmanypentachloli lddmm blfluorldo..

1% sodium blfluorlde..

At moo.

AM 10 min. At once. 10

After 10 8 min. At once.

After 10 6 min. At once. 6

After 10 The mln. At once.

After 10 min.

The results of these tests unmistakably show, that in employing theproposed agents individually, the effect is far inferior'to thatattained by usin a mixture of carbon tetrachloride and so iumbifluoride. Naturally the molten metals are, in practice, not treated invacuo. Yet these tests show, that even under such severe conditions itis possible to attain the positive absence of pores, and therefore thepositive absence of gas in the molten metal by treatment in accordancewith the invention.

The small amount of the agent required allows now, also to employ inpractice those chlorides hitherto considered to be too expensive, suchas vanadium chloride, boron trichloride and titanium tetrachloride. Indoing this the particular advantage is attained, that a minute quantityof thetitanium, or the vanadium contained in the salt forms an allo withthe aluminium, causing a finer grain 1n the casting. Simultaneously theMS]! of an absolute purification of the treated metal causing coarsecrystals in the castings is hereby avoided.

The finally mentioned chlorides of iron, tin, or zinc, naturally mayonly be employed in such cases, in which the entrance of zinc, tin, oriron into the alloy are of no detrimental influence. When for example itis intended to purify 'an aluminium-sandcasting alloy containing zincone-may use zinc chloride in admixture with carbon tetrachloride orantiinony pentachloride and alkalibifluorid'e, because the individualaction of zinc chloride is not so intensive as that of its mixturesmentioned. Herewith however an appreciable savin in the working expensesis attained, zinc c oride being obtainable at a low price.

A suitable re ration for -a bath of molten alu iiiinium only is composedas follows:

This preparation is filled into an aluminof the ha is to be treated, andis charged with one tube g ium tube of about 20-25 g. capacity. Themetal which ma .have been considerably overheated is coo ed down to'750"C.. The

,immersin device is chosen to'suit the shape containing the molten metalwhich perevery 20 kg. of metal. It is then immersed into the metal bathand removed when the reaction has ceased. During the sub- 7 sequentwaiting time of 10 minutes the temperature should drop to 730 C. Thenthe dross is skimmed off and' the metal is taken out of the furnace andcast. i

For an alloy of the composition Si 13% Al 23 remainder the followingmixture has been found suitable:

' Per cent Carbon tetrachloride 50 Ammonium bifluoride 10 Borontrichloride 5 Antimony pentachloride 10 Manganous chloride Infusorialearth; 10

German alloy is suitably purified with the following mixture:

' Percent Carbon tetrachloride 50 Ammonium bifluoride 10 Zincchloride 4Infusorial earth 10 For American alloy containing Cu 8% Al remainder,Y-alloy containing Cu 4%, N1 2%, Ng 1.5%, A1 remainder, and similar alloys, for example, the following mixture may be used:

Ifthe separation ofgases and oxides is intended for example'from an alloof alumin- 5 ium containing about 0.5% antimony, 1.4%

manganese, 2% magnesium, so as to attain a good castibility, it issufiicient to use 1 to 2 per thousand of the weight of the alloy of theabove named salts.

7 The chlorides which occur in the liquid cause the latter can be groundto an exceed state are preferably allowedto be soaked up by inertmaterial before'they are applied. Besides charcoal powder, infusorialearth is particularly suitable for this purpose, be-

l en-cent in ly fine wder and possesses a good abso ptivity lf thechlorides are not in the li uid state infusorial earth is also asuitable admixture, because it has a saving efiect upon the consumptionof material, causing the more volatile chlorides not tobe releasedbefore a certain time of their action has elapsed. Therefore the actionu n the molten metal is more intensive and on r lasting, if thechlorides are mixed with infusorial earth or soaked into it. Similar tothe action of infusorial earth, though not quite as favourable, is thatof asbestos wool.

Since a satisfactory effect of the purifying material can only beattained if the chlorine as liberated or formed from the chlorides 18caused to penetrate into the whole mass of the molten metal, it has beenfound desirable to use a special device for introduoin the material intothe molten metal. This evice is shown in the accompanying drawin In thefi ure (1) denotes a semicircular be provide with holes (2) at the sideto allow the escape of gases, and in the centre of it a pointed plunginrod (3). The point 34) of the plunging rot? is provided wi h bear s 5 toallow a firm fastening of the shell 7 which is preferably an aluminiumtube, fil ed with the purifying material (6). The other end of the plunng rod is bent at a right angle and provi ed with the handle (8) so asto allow the workmen calmly and steadily to insert the purifyingmaterial without being spattered or molested by the rising fumes.

The bell which is firmly connected with the plunging rod serves thepurpose of preventing the chemicals from rising u and of allowing the.evolved gases to be istributed in the molten metal and to escape.

In case of metal baths being shallow, it is advisable to unite aplurality of these bells with each other, forming an aggregate which issimultaneously charged and introduced into the metal.

After the reaction has taken place and after a short waiting-time theslags are taken OK and the metal maybe cast.

I claim:

1. A process for removing oxides and gases from molten aluminium andaluminium alloys which com rises treating the molten metal with apurifying agent consisting of a chloride which produces a gaseousproduct at the temperature of treatment and a volatile fluoride of thegroup consisting of alkali 3. A process for removing oxides and gasesfrom molten aluminium and alumimum alloys which comprises treating themolten metal with a purifying aglentpf the group consisting of carbontetrac loride, antimony pentachloride, manganous chloride, zinc chlorideand silicon tetrachloride and ammonium bifluoride.

at the temperature of treatment and a volatilefluoride of the groupconsisting of alkali metal and ammonium bifluorides together with achloride of ametal which alloys with the molten metal causing a finergrain in the cast metal.

6. A process for removing oxides and gases from molten aluminium andaluminium alloys which comprises treating the molten metal with aurifying agent consisting of a chloride which produces a gaseous productat the temperature of treatment and a volatile fluoride of the groupconsisting of alkali metal. and ammonium bifluorides together with achloride of a metal selected from the group consistin of vanadium andtitanium.

7. A process or removing oxides and gases from molten aluminium andaluminium alloys which comprises treating the molten metal with aurifying agent consisting of carbon tetrachlhride, a chloride of thegroup consisting of antimon pentachloride, manganous chloride, zinc cloride and silicon tetrachloride and a volatile fluoride of the groupconsisting of alkali metal and ammonium b1- 8. A process for removingoxidesand gases from molten aluminum and aluminum alloys which comprisestreating the molten -metal with a purifying agent consistin of achloride which produces a gaseous pr uct at the temperature of treatmentand a volatile fluoride of the grou consisting of alkali metal andammonium-bi uorides, said purifying agent being associated with an inertabsorptlve material.

9. A process for removing oxides and gasesfrom molten aluminium andaluminium alloys which com rises treating the molten metal with a uriying agent consisting of a chloride whic produces a gaseous product.

at the temperature of treatment and a volatile fluoride of the groupconsisting of alkali metal and ammonium bifluorides, said purifyingagent being associated with infusorial' 10. A composition for removing Ioxides and gases from molten aluminium and aluminium alloys comprising-achloride which produces a gaseous product at the temperature of themolten metal and a volatile fluo-' ride of the group consisting ofalkali metal chloride, antimony pentac oride, man anous chloride, zincchloride, silicon tetrach oride, and ammonium bifluoride.

13. A composition for removing oxides and gases from molten aluminiumand aluminium alloys comprising carbon tetrachloride and ammoniumbifluoride.

.14.- A composition for removing oxides and gases from molten aluminiumand aluminium alloys comprising a chloride which produces a gaseousproduct at the temperature of the molten metal and a volatile fluorideof the grou consisting of alkali metal and ammonium ifluorides, togetherwith a chloride of a metal which alloys with the molten metal causing afiner grain in the cast metal.

15. A composition for removing oxides and gases from molten aluminiumand aluminium alloys comprising a chloride which produces a gaseousproduct at the temperature of the molten metal and a volatile fluorideof the group consisting of alkali metal and ammonium bifluorides,together with a chloride of a metal selected from the groupconsisting'of vanadium and titanium.

' 16. A composition for removing oxides and gases from molten aluminiumand aluminium alloys comprising carbon tetrachloride, a chloride of thegroup consisting of antimony pentachloride, manganous chloride, zincchloride and silicon tetrachloride, and a volatile fluoride of the groupconsistof alkali metal and ammonium bifluor- 1 es.

17. A composition for removing oxides and gases from molten aluminiumand aluminium alloys comprising a chloride which produces a gaseousproduct at the temperature of the molten metal, and a volatile fluorideof the group consisting of alkali metal and ammonium bifluorides, saidpurifying agent being associated with an inert absorptive material.

18. A composition for removing oxides and gases from molten aluminiumand aluminium alloys comprising a chloride which produces a gaseousproduct at the temperature of the molten metal, and a volatile fluorideof the group consisting of alkali metal and ammonium bifluorides, saidpurifying agent being associated with infusorial earth.

In testimony whereof, I afiix my signature.

ROLAND STERNER-RAINER.

